1. Field of the Invention
The invention relates to a pressure gauge, more particularly, to a pressure gauge having marked means thereon which can be pre-arranged so as to indicate a predetermined pressure of a pneumatic tire and at the same time relieve excessive pressure by releasing air from the same.
2. Description of the Related Art
Pressure gauges can generally be divided into two kinds. The first kind is a pen-type, and the other type has pressure indicator on a scale board. Presently, pen-type pressure gauges are much more convenient to use and are preferred by many users. They mainly includes a valve means and a slide means therein, such that when the valve means is connected to an inflating valve of a pneumatic tire, the pressure of which we want to know, the slide means slides out of the pressure gauge indicating the pressure of the pneumatic tire.
There exist already several kinds of pen-type pressure gauges in the market. Each of them, though, can indicate the pressure of a connected tire, but lacks a means to relieve excessive pressure if there should be any. Besides, said pressure gauge can not be pre-arranged to show the required or optimum amount of pressure of a connected tire.